Seal device

ABSTRACT

[PROBLEMS] A seal device where a seal lip reliably maintains shaft sealing relative to high-pressure fluid that is to be sealed and where the equivalent Mises stress occurring in the seal lip is reduced to extend the durable term of the seal lip longer. 
     [MEANS FOR SOLVING PROBLEMS] A backup ring ( 2 ) has a tapered section ( 23 ) continuously extending from a fixation section ( 21 ) of the backup ring ( 2 ) and also has a forward end section ( 24 ). A rounded surface (E) with a curvature radius (R-1) is formed at least at a boundary ( 26 ) where a surface (D) of the tapered section ( 23 ) changes to a surface (F) of the forward end section ( 24 ). A portion of the surface (D) of the tapered surface ( 23 ), which portion is in contact with the rounded surface (E) at the boundary ( 26 ), is a projected curvature surface having a curvature radius greater than the curvature radius (R-1) of the boundary ( 26 ).

TECHNICAL FIELD

The present invention relates to a seal device for sealing a shaft, theseal device having a seal lip; and particularly relates to a seal devicewherein a seal lip can establish a reliable shaft seal relative to ahigh-pressure coolant or another such sealed fluid, and wherein theservice life of the seal lip can be extended to a longer period of time.

BACKGROUND ART

Recently, coolants used in car air conditioners and the like are beingchanged from CFC gas to carbon dioxide gas for the sake of environmentalimpact, and structures for shaft sealing carbon dioxide gas as a sealedfluid have been becoming more common. However, in cases in which carbondioxide gas is used for the coolant, the sealed fluid that will be thecoolant is set to higher pressures than have been used in the past.There has arisen an urgent need to improve the sealing strength of theshaft sealing portion, and various seal devices having high sealingstrength have been developed as lip seals for compressors in car airconditioners.

One example is a lip seal device (see FIG. 10) disclosed in UtilityModel Application No. 3-41264 (Patent Document 1).

In this lip seal device, a backup ring 103 made of a metal material andhaving a ring shape is disposed between a rotating shaft 102 and aninternal peripheral surface on the atmosphere side of a seal lip 101,the backup ring 103 being fitted in light contact with the internalperipheral surface of the seal lip 101. Furthermore, an annular part 104made of a resin material is disposed in the same shape as the backupring 103 on the atmosphere side B of the backup ring 103. Furthermore,on a fluid storage chamber side A of the backup ring 103, a seal surface107 a firmly bonded to the external peripheral surface of the rotatingshaft 102 is provided to an end part 107 at which the seal lip 101extends slantwise towards the fluid storage chamber from a proximal part106 in which a reinforcing ring 105 is embedded, and a garter spring 108for subjecting the seal surface 107 a to tension is mounted in anannular groove provided to the external peripheral surface of the endpart 107.

A ring-shaped support plate 109 is disposed on the atmosphere side ofthe annular part 104, and the backup ring 103, the annular part 104, andthe support plate 109 are sandwiched together by a holding ring 110whose external periphery has a U shape in cross section. These threesandwiched components collectively are a sealing part that reinforcesthe aligned seal lip 101.

The distance between the annular groove and the seal surface 107 a atthe distal end of the seal lip 101 must be reliably manufactured, butthe seal lip 101 easily deforms, being made of rubber, and it isdifficult to ensure the dimension of this distance when the rubber ismolded. Furthermore, the backup ring 103 and the seal lip 101 must bereliably joined together, and when the backup ring 103 is pressed intothe seal lip 101, the sealing capacity is compromised because the seallip 101 is lifted up off the external peripheral surface of the rotatingshaft.

To resolve this variety of problems, techniques have been developed suchas those demonstrated in Japanese Patent No. 3346743 (Patent Document 2)and Japanese Laid-open Patent Application No. 2003-120821 (PatentDocument 3). In the disclosed techniques, an inclined supporting part ofa backup ring is press-fitted into a tapered surface in a seal lip toexpand the diameter of the sealing part surface, the enlarged taperedsurface of the inclined seal lip is held in pressured contact by theinclined supporting part, and the sealing part surface on the atmosphereside is maintained at a constant angle. According to this type ofconfiguration, the sealing part surface held under tension by the backupring is firmly bonded with sharp surface pressure to the externalperipheral surface of the shaft, the sealing part surface is in contactwith the shaft across a small contact surface area, the sealing capacityis effectively prevented from decreasing as a result of abnormaldeformation in which the sealing part surface is jammed, the state ofthe sealing corner being in contact under sharp surface pressure ismaintained, and excellent sealing capacity is exhibited.

Patent Document 1: Utility Model Application No. 3-41264 (pg. 1, FIG. 1)

Patent Document 2: Japanese Patent No. 3346743 (pg. 2, FIG. 2)

Patent Document 3: Japanese Laid-open Patent Application No. 2003-120821(pg. 2, FIG. 1)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in conventional techniques such as those disclosed in JapanesePatent No. 3346743 (Patent Document 2) and Japanese Laid-open PatentApplication No. 2003-120821 (Patent Document 3), when a large amount ofsealed fluid pressure is applied to the external periphery of the rubberseal lip, the seal lip is pressed towards the rotating shaft, andexcessive stress is created between the corner where the tapered surfaceof the backup ring folds back toward the rotating shaft and the sealinginside surface of the seal lip. An extremely large amount of equivalentMises stress is created in the seal lip located at the corner of thebackup ring, and with long-term use, there is a danger that the seal lipwill suffer fractures. In practice, although roundness (R) is formed inthe corner of the backup ring described above and efforts are made toreduce the equivalent Mises stress created in the seal lip, yet afurther reduction in the equivalent Mises stress is desired.

The present invention was designed in view of problems such as thosedescribed above, and an object thereof is to provide a seal devicewherein a seal lip can maintain a reliable shaft seal relative to ahigh-pressure sealed fluid, the equivalent Mises stress created in theseal lip can be reduced, and the service life of the seal lip can beextended to a longer period of time.

Means for Solving These Problems

To solve these problems, the seal device according to a first aspect ofthe present invention is a seal device having a backup ring protrudingtowards a fluid storage chamber so as to enclose a rotating shaft,wherein at least the backup ring has a tapered shape, and a distal endof a seal lip supported by the backup ring is capable of coming intocontact with the rotating shaft; the seal device characterized in thatthe backup ring has a tapered part and a distal end part extendingcontinuously from a fixed part thereof; a rounded surface having acurvature radius (R-1) is formed at least in a boundary where a surfaceof the tapered part changes to a surface of the distal end; and part ofthe surface of the tapered part adjacent to the rounded surface at theboundary is a convex surface having a curvature radius greater than thecurvature radius (R-1) of the boundary.

According to these characteristics, pressure from the fluid storagechamber side acts on the seal lip, and the lip distal end is pressedagainst the rotating shaft, while pressing force from the seal lip isexerted on the backup ring at the same time. The seal lip in particularthen comes firmly into contact with the boundary (corner of the backupring) where the surface of the tapered part of the backup ring changesto the surface of the distal end, and there is a tendency for anextremely large amount of equivalent Mises stress to accumulate at thislocation. However, according to the present invention, since a surfacethat is not a straight linear surface and that has a comparatively largecurvature radius is formed in part of the surface of the tapered partconnected to the rounded surface at the boundary, the swelled roundness(curvature radius) of at least part of the tapered part contributes toincreasing the surface area of the tapered part of the backup ring forholding the seal lip, and although pressure from the fluid storagechamber acts on the seal lip due to the increase in frictional force ofthis enlarged contact surface, slight misalignments are effectivelyprevented from occurring between the seal lip and the tapered surface ofthe backup ring. Therefore, an extreme amount of equivalent Mises stressdoes not accumulate in the seal lip located at the boundary (corner ofthe backup ring) where the surface of the tapered part of the backupring changes to the surface of the distal end, the equivalent Misesstress occurring in the seal lip can be reduced while a reliable shaftseal is maintained by the seal lip, and the service life of the seal lipcan be extended to a longer period of time.

The seal device according to a second aspect of the present invention isa seal device having a backup ring protruding towards a fluid storagechamber so as to enclose a rotating shaft, wherein at least the backupring has a tapered shape, and a distal end of a seal lip supported bythe backup ring is capable of coming into contact with the rotatingshaft; the seal device characterized in that the backup ring has atapered part and a distal end part extending continuously from a fixedpart thereof; a rounded surface having a curvature radius (R-1) isformed at least in a boundary where a surface of the tapered partchanges to a surface of the distal end; and the surface of the taperedpart is a convex surface having a substantially constant curvatureradius (R-2) greater than the curvature radius (R-1) of the boundary.

According to these characteristics, the surface of the tapered part is atapered surface having a tapered end and a substantially constantcurvature radius (R-2) greater than the curvature radius (R-1) of theboundary, whereby the curvature radius (R-2) contributes to increasingthe surface area of the tapered part of the backup ring for holding theseal lip, and although pressure from the fluid storage chamber acts onthe seal lip, slight misalignments can be effectively prevented fromoccurring between the seal lip and the tapered surface of the backupring. Therefore, an extreme amount of equivalent Mises stress does notaccumulate in the seal lip located at the boundary (corner of the backupring) where the surface of the tapered part of the backup ring changesto the surface of the distal end, the equivalent Mises stress occurringin the seal lip can be reduced while a reliable shaft seal is maintainedby the seal lip, and the service life of the seal lip can be extended toa longer period of time.

The seal device according to a third aspect of the present invention isthe seal device according to the second aspect, the seal devicecharacterized in that the backup ring has a protruding part extendingcontinuously from a fixed part thereof, wherein the surface of theprotruding part is substantially parallel to the rotating shaft; and theboundary where the surface of the protruding part changes to the surfaceof the tapered part is a rounded surface having a curvature radius equalto or greater than the curvature radius (R-2) of a tapered surface whichis the surface of the tapered part.

According to these characteristics, in conventional practice, when acurved part having a comparatively small curvature radius is present inthe boundary where the surface of the protruding part changes to thesurface of the tapered part in the backup ring, fluctuations in theinternal pressure of the fluid storage chamber are likely to cause theseal lip to detach from the backup ring at this curved part, and slightmisalignments occur more readily between the seal lip and the taperedsurface of the backup ring. However, according to the configurationdescribed above, a boundary can be formed where the surface of theprotruding part gently changes to the surface of the tapered part;therefore, there is no extremely curved part, and slight misalignmentscan be effectively prevented from occurring between the seal lip and thetapered surface of the backup ring.

The seal device according to a fourth aspect of the present invention isa seal device having a backup ring protruding towards a fluid storagechamber so as to enclose a rotating shaft, wherein at least the backupring has a tapered shape, and a distal end of a seal lip supported bythe backup ring is capable of coming into contact with the rotatingshaft; the seal device characterized in that the backup ring has atapered part and a distal end part extending continuously from a fixedpart thereof; a rounded surface having a curvature radius (R- 1) isformed at least in a boundary where a surface of the tapered partchanges to a surface of the distal end; and the surface of the taperedpart is a convex surface that has no linear surfaces and that iscomposed of a combination of a plurality of different curvature radiigreater than the curvature radius (R-1) of the boundary.

According to these characteristics, the surface of the tapered part is atapered surface having a tapered end and having no straight linearsurfaces, the surface being composed of a combination of a plurality ofdifferent curvature radii greater than the curvature radius (R-1) of theboundary, whereby the curvature can be varied so as to adapt to thepressure distribution inside the fluid storage chamber, and slightmisalignments can be effectively prevented from occurring between theseal lip and the tapered surface of the backup ring.

The seal device according to a fifth aspect of the present invention isthe seal device according to any of the first through fourth aspects,characterized in that an inside end surface substantially parallel tothe rotating shaft is formed in the distal end of the backup ring; and arounded surface having a curvature radius (R-0) less than that of therounded surface having the curvature radius (R-1) is formed in theboundary where the surface of the distal end changes to the inner endsurface.

According to these characteristics, the seal lip is not damaged at thecorner of the inside end surface of the distal end of the backup ring.

The seal device according to a sixth aspect is the seal device accordingto any of the first through fifth aspects, characterized in that theinside surface of the seal lip, which is supported by the backup ringhaving the protruding part, the tapered part, and the distal end partextending continuously from the fixed part, is formed in advance, atleast when the seal lip is molded, as a concave surface to fit with theconvex surface of the tapered part of the backup ring.

According to these characteristics, the seal lip is formed in advance asa concave rounded surface for fitting with the convex rounded surface ofthe tapered part of the backup ring; therefore, slight misalignments canbe effectively prevented from occurring between the seal lip and thetapered surface of the backup ring, depending on the material strengthof the seal lip itself.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a semi-cross-sectional view of the seal device in the firstembodiment of the present invention;

FIG. 2 is a perspective view of the backup ring;

FIG. 3 is a cross-sectional view of the top half of the backup ring;

FIG. 4 contains drawings showing the measurement (Test 1) of theequivalent Mises stress achieved with the backup ring, and an experiment(Test 2) for evaluating the likelihood of the seal lip to break;

FIG. 5 contains drawings showing the results of Test 1;

FIG. 6 is a diagram showing the results of Test 2;

FIG. 7 contains drawings comparing the backup rings of the firstembodiment and Comparative Example 3;

FIG. 8 is a drawing showing the structure of the seal lip;

FIG. 9 is a drawing showing the seal device of the second embodiment;and

FIG. 10 is a drawing showing the lip seal device disclosed in UtilityModel Application No. 3-41264 (Patent Document 1).

KEY

1 seal device

2 backup ring

3 seal lip

4 seal lip

5 seal lip

6 housing

7 fitting part

7A sealing portion

8 reinforcing ring

21 fixed part

22 protruding part

23 tapered part

24 distal end

26 boundary

27 inside end surface

29 boundary

31 lip distal end

32 concave surface

50 rotating shaft

61 fitting hole

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are described hereinbelow.

Embodiments

Embodiments of the present invention shall be described with referenceto the drawings. First, FIG. 1 is a semi-cross-sectional view of theseal device in the first embodiment of the present invention. FIG. 2 isa perspective view of the backup ring. FIG. 3 is a cross-sectional viewof the top half of the backup ring. FIG. 4 contains drawings showing themeasurement (Test 1) of the equivalent Mises stress achieved with thebackup ring, and an experiment (Test 2) for evaluating the likelihood ofthe seal lip to break. FIG. 5 contains drawings showing the results ofTest 1. FIG. 6 is a diagram showing the results of Test 2. FIG. 7contains drawings comparing the backup rings of the first embodiment andComparative Example 3. FIG. 8 is a drawing showing the structure of theseal lip. FIG. 9 is a drawing showing the seal device of the secondembodiment. FIG. 10 is a drawing showing the lip seal device disclosedin Utility Model Application No. 3-41264 (Patent Document 1).

FIG. 1 shows the seal device of the first embodiment according to thepresent invention, and is a semi-cross-sectional view of a state inwhich the seal device is not attached to a shaft. In FIG. 1, thenumerical symbol 1 denotes a seal device installed between an atmosphereY side and a fluid storage chamber X side, and this seal device 1 isprovided with a rubber fitting part 7 for fitting into a fitting hole 61in a housing 6. A convex-shaped sealing portion 7A is formed on theexternal peripheral surface of the fitting part 7. A reinforcing ring 8is embedded within the fitting part 7. The fitting with the housing 6 isstrengthened by this reinforcing ring 8, and a second seal lip 4 andthird seal lip 5 are held by the fitting part 7.

A rubber seal lip 3 is formed into a cylinder shape that slants from thefitting part 7 towards a rotating shaft 50, with the reinforcing ring 8interposed therebetween. A lip distal end 31 of the seal lip 3constitutes a sealing function surface and exhibits a sealing capabilityby increasing surface pressure when optimally bonded to the rotatingshaft 50.

The side of the seal lip 3 that faces the fluid storage chamber X fromthe fitting part 7 is provided with a backup ring 2 having a shapesubstantially resembling the seal lip 3 along the surface of the seallip 3. This backup ring 2 is formed to a thickness that ispressure-resistant enough to not deform despite the pressure of thesealed fluid acting on the seal lip 3.

In the seal device 1 of the first embodiment, the backup ring 2, whichprotrudes towards the fluid storage chamber X so as to enclose therotating shaft, has a tapered shape in at least the front portion of thebackup ring as shown in FIGS. 1 and 2, and the lip distal end 31 of theseal lip 3 supported by the backup ring 2 is capable of being in contactwith the rotating shaft 50. The backup ring 2 of the seal device 1 has afixed part 21, which is a portion fixed to the seal device 1 due tobeing sandwiched by the second seal lip 4 and the rubber seal lip 3supported by the reinforcing ring 8.

Furthermore, the backup ring 2 has a protruding part 22, a tapered part23, and a distal end part 24 which extend continuously from the fixedpart 21. FIG. 3 shows a cross-sectional view of the top half of thebackup ring 2, wherein the surfaces of the parts are shown sequentiallyas a surface A of the fixed part 21, a surface B of the protruding part22, a surface D of the tapered part 23, and a surface F of the distalend 24. A rounded surface E having a curvature radius (R-1) is formed atleast on a surface of a first boundary 26 where the surface D of thetapered part 23 changes to the surface F of the distal end 24, and arounded surface C having a curvature radius (R-3) is formed on a surfaceof a second boundary 29 where the surface B of the protruding part 22changes to the surface D of the tapered part 23. In the seal device ofthe first embodiment, the entire surface D of the tapered part 23 inparticular is formed into a tapered surface composed of a convex surfacehaving a substantially constant curvature radius (R-2) greater than thecurvature radius (R-1) of the rounded surface E of the first boundary26. Furthermore, the rounded surface C, which is the surface of thesecond boundary 29 where the surface B of the protruding part 22 changesto the surface D of the tapered part 23, is also formed into a convexsurface having the same curvature radius (R-2) as the curvature radius(R-2) of the surface D of the tapered part 23. In this case, when thecurvature radius (R-3) of the rounded surface C and the curvature radius(R-2) of the surface D of the tapered part 23 are the same curvatureradii, the rounded surface C and the surface D of the tapered part 23are easily worked, and the surface B of the protruding part 22 canchange to the surface D of the tapered part 23 via merely a slightlycurved surface.

Without being limited to the present embodiment, it is sufficient toform a convex surface having a curvature radius (R-2) greater than thecurvature radius (R-1) of the rounded surface E of the first boundary 26on only part of the surface D of the tapered part 23 that continues tothe rounded surface E, which is the surface of the first boundary 26.Specifically, in the present invention, a straight surface in thesurface D of the tapered part 23 need only be made as small as possible,and the swelled roundness (curvature radius) of at least part (or all)of the tapered surface of the backup ring 2 can contribute to increasingthe surface area of the tapered surface of the backup ring 2 for holdingthe seal lip 3.

In cases in which a convex surface having a curvature radius (R-2)greater than the curvature radius (R-1) of the rounded surface E of thefirst boundary 26 is formed in only part of the surface D of the taperedpart 23, it is more preferable to form a convex surface having acurvature radius (R-2) greater than the curvature radius (R-1) of therounded surface E in the part of the surface D of the tapered part 23near to the rounded surface E, because this convex surface will belikely to affect the proximity of the rounded surface E.

Furthermore, an inside end surface 27 substantially parallel to therotating shaft 50 is formed in the distal end 24 of the backup ring 2,and a rounded surface F′ having a curvature radius (R-0) less than thecurvature radius (R-1) of the rounded surface E of the first boundary 26is formed in the portion where the surface F of the distal end 24changes to the inside end surface 27. Regarding the distal end 24, thesurface F of the distal end 24 is oriented essentially perpendicular tothe rotating shaft 50, and instead of providing a perpendicular surfacethereto, the surface F of the distal end 24 may be a curved surfacewhere the rounded surface E having a curvature radius (R-1) changesdirectly to the rounded surface F′ having a curvature radius (R-0). Theresult of the presence of at least the rounded surface F′ having acurvature radius (R-0) is that the seal lip 3 is not damaged by thecorner formed at the inside end surface of the distal end 24 of thebackup ring 2.

In the seal device of the first embodiment, as suitable examples, thecurvature radius (R-0) of the rounded surface F′ is 0.1 mm, thecurvature radius (R-1) of the rounded surface E is 0.4 mm, the curvatureradius (R-2) of the surface D is 3.0 mm, and the curvature radius (R-3)of the rounded surface C is 3.0 mm.

In the backup ring 2 in the seal device of the first embodiment, thesurface R of the protruding part 22 extending continuously from thefixed part 21 is substantially parallel to the rotating shaft 50, andthe rounded surface C, which is the surface of the second boundary 29where the surface B of the protruding part 22 changes to the surface Dof the tapered part 23, may be a rounded surface having a curvatureradius (R-3) greater than the curvature radius (R-2) of the surface D ofthe tapered part 23. Furthermore, the shape of the fixed part 21 isarbitrary, and not only is there no need for the surface B of theprotruding part 22 to be substantially parallel to the rotating shaft50, but there is also no need to separately distinguish between thefixed part 21 and the protruding part 22.

Generally, as previously described, in cases in which a large amount ofsealed fluid pressure is applied to the external periphery of the rubberseal lip 3, the seal lip 3 is pushed in the axial direction of therotating shaft 50, excessive stress is created between the sealinginternal surface of the seal lip 3 and the corner (proximity of therounded surface E) where the tapered surface of the backup ring 2 foldsback towards the rotating shaft, and the equivalent Mises stress isapplied to the seal lip 3 located in proximity to the rounded surface E.Measurements were taken (Test 1) of the equivalent Mises stress achievedwith the backup ring 2 of the seal device (present invention) of thefirst embodiment, and of the equivalent Mises stress achieved when adifferently structured backup ring of Comparative Examples 1, 2, and 3was used; and an experiment (Test 2) was conducted for evaluating thelikelihood of the seal lip to break when subjected to pressurefluctuations and variations in temperature conditions, as shown in FIG.4.

(1) In Comparative Example 1 of the backup ring, a rounded surface C1 isa corner having substantially no roundness, and a surface D1is a flatsurface having substantially no roundness. (2) In Comparative Example 2of the backup ring, a rounded surface C2 has a curvature radius of 1.5mm, and a surface D2is a flat surface having substantially no roundness.(3) In Comparative Example 3 of the backup ring, a rounded surface C3has a curvature radius of 1.0 mm, and a surface D3is a flat surfacehaving substantially no roundness.

For the test conditions of Test 1, hot water was kept at a temperatureof 200° C., a pressure of 8 MPa was applied as the pressure of thesealed fluid, and the maximum equivalent Mises stress at the lip distalend due to the shapes of the backup rings was outputted as the result ofFEM analysis.

For the test conditions of Test 2, hot water was kept at a temperatureof 220° C., the pressure fluctuation range was set to 2 MPa, pressuresof 6 MPa and 8 MPa were alternately applied, and the pulse frequency wasset to 2400 times. Furthermore, for the eccentricity of the shaft, theaxial eccentricity was set to 0.3 mm, and the likelihood of the seal lipto break due to the shapes of the backup rings was evaluated.

For the results of Test 1, the maximum equivalent Mises stress at thelip distal end in Comparative Example 1 was 15.2 MPa, the maximumequivalent Mises stress at the lip distal end in Comparative Example 2was 13.3 MPa, the maximum equivalent Mises stress at the lip distal endin Comparative Example 3 was 8.3 MPa, and the maximum equivalent Misesstress at the lip distal end in the seal device (present invention) ofthe first embodiment was 7.9 MPa, as shown in FIG. 5. Furthermore,measuring the tension force (N) also confirmed that the seal device(present invention) of the first embodiment had a tension force (N) ofabout 184 N, which was less than the comparative examples, and the sealdevice was resistant to generated heat, as shown in FIG. 6.

The results of Test 2 showed that breakage occurred in all of the seallips in the other Comparative Examples 1, 2, and 3, whereas no breakageoccurred in the seal lip of the seal device (present invention) of thefirst embodiment, and it was clear that the equivalent Mises stress inthe seal lip could be reduced.

Referring to FIG. 7, the backup ring of the seal device of the firstembodiment is compared with the backup ring of Comparative Example 3,which comparatively resembles the first embodiment. Generally, whenpressure from the fluid storage chamber X side acts on the seal lip 3,the lip distal end is pressed against the rotating shaft, while at thesame time, pressing force from the seal lip 3 is exerted on the backupring 2. The seal lip 3 in particular then comes firmly into contact withthe boundary (corner of the backup ring) where the surface of thetapered part of the backup ring 2 changes to the surface of the distalend, and there is a tendency for an extremely large amount of equivalentMises stress to accumulate at this location.

According to FIG. 7, the surface D3in the tapered part of the backupring 2 in Comparative Example 3 is formed into a straight linearsurface. Furthermore, the rounded surface C3 is formed at the boundarybetween the surface B3 of the protruding part, which is a straightlinear surface extending continuously from the fixed part, and thesurface D3of the tapered part, which is a straight linear surface. Inthe backup ring 2 used in the seal device of the first embodiment, asurface that is not straight and linear and that has a comparativelylarge curvature radius is formed through all (or part) of the surface Dof the tapered part.

As is clear from the results of the comparative tests described above,the swelled roundness (curvature radius) of at least part (or all) ofthe tapered surface of the backup ring 2 used in the seal device of thefirst embodiment contributes to increasing the surface area of thetapered surface of the backup ring 2 for holding the seal lip 3, andalthough pressure from the fluid storage chamber X acts on the seal lip3 as a result of the frictional force of this enlarged contact surface,slight misalignments are effectively prevented from occurring betweenthe seal lip 3 and the tapered surface of the backup ring 2. Therefore,an extreme amount of equivalent Mises stress does not accumulate in theseal lip located at the rounded surface E of the first boundary 26 wherethe surface of the tapered part of the backup ring changes to thesurface of the distal end, the equivalent Mises stress occurring in theseal lip 3 can be reduced while a reliable shaft seal is maintained bythe seal lip 3, and the lip can be given a longer service life than thatof conventional products.

Particularly, in the seal device of the first embodiment, the entiresurface D of the tapered part 23 is formed into a tapered surface havinga tapered end and composed of a convex surface having a substantiallyconstant curvature radius (R-2) greater than the curvature radius (R-1)of the rounded surface E of the first boundary 26. Furthermore, therounded surface C, which is the surface of the second boundary 29 wherethe surface B of the protruding part 22 changes to the surface D of thetapered part 23, is also a convex surface having the curvature radius(R-2). In this case, the curvature radius (R-3) of the rounded surface Cand the curvature radius (R-2) of the surface D of the tapered part 23are the same curvature radius.

The backup ring 2 is easily manufactured if the curvature radius (R-3)of the rounded surface C and the curvature radius (R-2) of the surface Dof the tapered part 23 are the same curvature radius, but, not beinglimited to this option alone, the rounded surface C can also have acurvature radius (R-3) greater than the curvature radius (R-2) of thetapered surface, which is the surface of the tapered part.

Particularly, in the backup ring 2 of Comparative Example 3 or the like,the rounded surface C3 is realized as a comparatively conspicuous curvedpart in the boundary between the surface B3 of the protruding part,which is a straight linear surface extending continuously from the fixedpart, and the surface D3of the tapered part, which is a straight linearsurface. If the curved part having a comparatively small curvatureradius is present in this manner, fluctuations in the internal pressureof the fluid storage chamber are likely to cause the seal lip 3 todetach from the backup ring 2 at this curved part, and slightmisalignments are likely to occur between the seal lip 3 and the taperedsurface of the backup ring 2. However, in the seal device of the firstembodiment, the surface D of the tapered part already extends in aspecific curvature radius, and a boundary is formed where the surface Dof the tapered part gently changes to the surface B of the protrudingpart; therefore, there is no extremely curved part, and slightmisalignments can be effectively prevented from occurring between theseal lip 3 and the tapered surface of the backup ring 2.

FIG. 8 shows the structure of the seal lip 3, wherein the inside surfaceof the seal lip 3, which is supported by the backup ring 2 having aprotruding part, a tapered part, and a lip distal end part 31 extendingcontinuously from the fixed part, is formed in advance as a concavesurface 32 to fit with the convex curvature of the surface D of thetapered part of the backup ring 2, at least during the molding of theseal lip 3. When the seal lip 3 is formed in advance as a concavesurface 32 to fit with the convex surface D of the tapered part of thebackup ring 2, the concave surface 32 of the seal lip 3 and the convexsurface D of the tapered part thus fit together in the usual state ofpressure as well. Furthermore, the seal lip 3 is less prone todeformation than a conventional seal lip having a straight linearsurface on the inside surface, and slight misalignments can beeffectively prevented from occurring between the seal lip 3 and thetapered surface of the backup ring 2, depending on the material strengthof the seal lip 3 itself.

FIG. 9 shows the seal device of the second embodiment, which isdifferent from the seal device of the first embodiment in that in theseal device of the first embodiment, the entire surface D of the taperedpart 23 in particular is formed into a tapered surface having a taperedend composed of a convex surface having a substantially constantcurvature radius (R-2) greater than the curvature radius (R-1) of therounded surface E of the first boundary 26. In the seal device of thesecond embodiment, however, the surface D of the tapered part 23 iscomposed of surfaces D1, D2, D3. . . having different curvature radiithat are greater than the curvature radius (R-1) of the first boundary,and the surface D of the tapered part 23 is a tapered surface having atapered end with no straight linear surfaces, the surface being composedof a combination of different curvature radii. The curvature of thesurface D of the tapered part 23 can be varied greatly by combining thesurfaces D1, D2, D3 of different curvature radii so as to adapt to thepressure distribution inside the fluid storage chamber, and slightmisalignments can therefore be prevented from occurring between the seallip and the tapered surface of the backup ring.

When the surface is designed so as to gradually increase in curvatureradius from the rounded surface E of the first boundary 26, such thatthe relationship (curvature radius D1)>(curvature radius D2)>(curvatureradius of D3) is maintained, a boundary is then formed where the surfaceD of the tapered part gently changes to the surface B of the protrudingpart, and it is therefore unlikely for extremely curved parts to bepresent.

Embodiments of the present invention were described above with referenceto the accompanying drawings, but the specific configuration is notlimited to these embodiments, and the present invention incorporatesvariations and additions that do not deviate from the scope of thepresent invention.

1. A seal device having a backup ring protruding towards a fluid storagechamber so as to enclose a rotating shaft, wherein at least said backupring has a tapered shape, and a distal end of a seal lip supported bythe backup ring is capable of coming into contact with the rotatingshaft; said seal device characterized in that: said backup ring has atapered part and a distal end part extending continuously from a fixedpart thereof; a rounded surface having a curvature radius (R-1) isformed at least in a boundary where a surface of said tapered partchanges to a surface of said distal end; and the surface of said taperedpart is a convex surface that has no linear surfaces and that iscomposed of a combination of a plurality of different curvature radiigreater than the curvature radius (R-1) of said boundary.
 2. The sealdevice according to claim 1, characterized in that an inside end surfacesubstantially parallel to the rotating shaft is formed in the distal endof said backup ring; and a rounded surface having a curvature radius(R-0) less than that of the rounded surface having said curvature radius(R-1) is formed in the boundary where the surface of said distal endchanges to said inner end surface.
 3. The seal device according to claim2, characterized in that an inside surface of the seal lip, which issupported by said backup ring having the protruding part, the taperedpart, and the distal end part extending continuously from the fixedpart, is formed in advance, at least when said seal lip is molded, as aconcave surface to fit with the convex surface of the tapered part ofsaid backup ring.